Center Targets Two Pesky Diseases

As health challenges take their toll, a growing number of pork producers are demanding that researchers find ways to get rid of two pesky problems: Mycoplasmal pneumonia and porcine reproductive and respiratory syndrome (PRRS). That's the daunting task facing the Swine Disease Eradication Center (SDEC), says Carlos Pijoan, DVM, director of the two-year-old project.

Though much remains to be learned about how to stop disease transmission from sows to piglets, and the true value of treatment methods, Pijoan says vaccination seems to be adequately controlling mycoplasma infections.

PRRS remains a much stiffer challenge, however. Years ago, it was thought that PRRS would end up being like parvovirus, present in most herds but not a big deal, he recalls.

Then vaccines were developed. Their use has helped, but not proven to be a solution in every management program. Scott Dee, DVM, University of Minnesota and SDEC researcher, suggests the problem may be that producers don't know enough about herd immunity to apply the PRRS vaccines correctly.

Of late, producers have used a variety of cleanup plans to stamp out PRRS. The problem is, too many of those herds have become reinfected, says Dee.

Call for Action

When a flurry of PRRS outbreaks struck the Midwest last winter, they were unusual in that boar studs became infected — where biosecurity is paramount — as well as sow farms, notes Dee.

After that, the SDEC's 17-member industry advisory board put out an urgent call for some answers. The board, which helps support the center, includes some of the largest pork-producing operations, seedstock businesses and pharmaceutical firms in the country.

PRRS research was discussed at winter meetings. Dee and graduate student Satoshi Otake reviewed earlier work that showed aerosol transmission of the PRRS virus is all but non-existent. In their trials, they could not demonstrate airborne spread of the virus, even to pigs just one yard apart.

Other PRRS work they did at the SDEC research farm in west central Minnesota found that mosquitoes and houseflies could readily serve as mechanical vectors of the virus. Other work showed that treating sows using the same needle could spread the virus from sow to sow.

One big question was answered in a recent research project, reported on at the American Association of Swine Veterinarians annual meeting, by graduate student Laura Batista, DVM. She found that viral persistence in a breeding population is actually very short — probably less than 90 days.

“Everybody thinks PRRS is a never-ending infection like Herpes, but there is clear evidence now that it clears very quickly and there is no shedding after a period of time. That rolls in very nicely with how to acclimate gilts,” states Dee.

What remains a mystery is how both commercial herds and studs last winter came down with the virus, says Dee. A check of source and supplier herds indicated they were not the source of infection, for the most part.

“It appeared to be more of a lateral transmission, so we started thinking about cold weather and mechanical transmission,” he says.

That led Dee to his well-known “snowball” research which showed the virus could survive on snow-packed truck tires and be carried into a barn on boots with compacted snow.

The SDEC, acting on a directive from the advisory board, is conducting a full study of the incidence, distribution and spread of the PRRS virus transmission during last winter's epidemic, says Pijoan.

“I think the picture that is emerging with PRRS certainly is that you can transmit it readily and easily with bodily fluids, but you cannot transmit it readily without those factors,” observes Pijoan.

Additional center research proposals have been funded as well.

Targeting Mycoplasma

Mycoplasma is also not readily spread, says Pijoan. In one trial, Batista and other students tested and handled a large number of pigs that had mycoplasma. Researchers showered, changed clothes and went directly to a PRRS-positive gilt farm known to be mycoplasma negative. Despite following this procedure eight different times, 15 days apart, the replacement gilts remained negative for mycoplasma, Pijoan explains.

For PRRS and mycoplasma, the SDEC is starting over to get the basic facts about these two important swine diseases, explains Dee. Not much is actually known. “It's like driving a car with a blindfold. You can't really see where you are going, or what's coming,” he says.